The present invention relates to a thermoplastic resin composition. More particularly, the present invention relates to a thermoplastic resin composition which is low in rigidity such as tensile strength, so ductile that its molded product shows no sharp edge on rupture cross-section upon collision, has a high resistance to thermal deformation and exhibits an excellent moldability.
Because of its excellent impact resistance, thermal deformation resistance and moldability, an ABS resin (acrylonitrile-butadiene-styrene) finds wide application to automobile interior and exterior materials, housing and parts of household electrical appliances, and office automation equipments etc. In recent years, automobile interior and exterior materials have been required to provide safety upon collision such as side collision regulation that the rupture cross-section developed by collision must not show sharp edge in addition to excellent properties such as high temperature dimensional stability and external surface appearance.
In order to satisfy these requirements, many studies have been made. However, no ABS resins having satisfactory properties have been obtained. For example, JP-A-59-20346 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses an approach involving the addition of a specific plasticizer to a rubber-reinforced styrene resin. However, this approach leaves something to be desired because the resulting resin composition exhibits a deteriorated thermal deformation resistance and the plasticizer can evaporate. The use of a polypropylene-based resin having a specific composition has been studied. However, this approach is disadvantageous in that the resulting molded product has an impaired external surface appearance due to sinking, a deteriorated dimensional stability due to warpage and a deteriorated adhesion to other materials. Further, it has been practiced to fill the interior of these parts with a foamed polyethylene product. However, this approach is disadvantageous in that the production process is complicated and gives a poor economy.
Paying attention to the distribution of particle diameter of rubber in styrene-based resin, a method for improving impact resistance has been proposed. For example, JP-A-8-134312 and JP-A-8-134316 propose the combined use of a small particle diameter rubber and a middle particle diameter rubber.
However, none of these approaches provide a resin composition which exhibits a low rigidity, shows a ductile rupture cross-section in the form of molded product and has a high thermal deformation resistance and an excellent moldability.
The present invention gives solution to the foregoing problems and provides a thermoplastic resin composition which is low in rigidity such as tensile strength, so ductile that its molded product shows no sharp edge on rupture cross-section, has a high resistance to thermal deformation and exhibits an excellent moldability.
The inventors made extensive studies of solution to the foregoing problems with ABS resin. As a result, it was found that a thermoplastic resin composition having a great rubber content comprising (A) a specific graft copolymer containing a rubber having a small particle diameter and (B) a specific graft copolymer containing a rubber having a middle particle diameter incorporated therein in a specific proportion and comprising a (D) styrene-based copolymer having a low molecular weight incorporated therein is low in rigidity such as tensile strength, so ductile that its molded product shows no sharp edge on rupture cross-section, has a high resistance to thermal deformation and exhibits an excellent moldability. Thus, the present invention has been worked out.
The present invention lies in a thermoplastic resin composition having a rubber content of from 25 to 50% by weight based on the resin composition comprising from 2 to 20 parts by weight of a copolymer (A), from 30 to 68 parts by weight of a copolymer (B), from 5 to 35 parts by weight of a copolymer (C) and from 25 to 63 parts by weight a copolymer (D), totaling 100 parts by weight.
(A) Graft Copolymer Containing a Rubber Having a Small Particle Diameter
A graft copolymer obtained by the polymerization of from 40 to 90 parts by weight of at least one rubber polymer (R) selected from the group consisting of diene-based rubber polymer, acrylic rubber polymer, silicon-based rubber polymer and olefinic rubber polymer having a volume-average particle diameter of from 60 to 160 nm with from 10 to 60 parts by weight of a monomer mixture comprising from 10 to 90% by weight of an aromatic vinyl compound, one or more of a (meth)acrylic acid ester and a vinyl cyanide compound in an amount of from 10 to 90% by weight, and from 0 to 30% by weight of a monomer copolymerizable therewith, totaling 100% by weight;
(B) Graft Copolymer Containing a Rubber Having a Middle Particle Diameter
A graft copolymer obtained by the polymerization of from 40 to 90 parts by weight of at least one rubber polymer (R) selected from the group consisting of diene-based rubber polymer, acrylic rubber polymer, silicon-based rubber polymer and olefinic rubber polymer having a volume-average particle diameter of from 300 to 800 nm with from 10 to 60 parts by weight of a monomer mixture comprising from 10 to 90% by weight of an aromatic vinyl compound, one or more of a (meth)acrylic acid ester and a vinyl cyanide compound in an amount of from 10 to 90% by weight, and from 0 to 30% by weight of a monomer copolymerizable therewith, totaling 100% by weight;
(C) xcex1-Methylstyrene and/or Maleimide-based Copolymer
An xcex1-methylstyrene and/or maleimide-based copolymer having a methyl ethyl ketone soluble content reduced viscosity of from 0.45 to 1.2 dl/g (as determined at 30xc2x0 C. in N,N-dimethylformamide solution) obtained by the polymerization of a monomer mixture comprising from 10 to 40% by weight of acrylonitrile, xcex1-methylstyrene and/or maleimide in an amount of from 5 to 80% by weight, from 0 to 85% by weight of styrene, and from 0 to 20% by weight a monomer copolymerizable therewith, totaling 100% by weight; and
(D) Styrene-based Copolymer
A styrene copolymer having a methyl ethyl ketone soluble content reduced viscosity of from 0.20 to 0.45 dl/g (as determined at 30xc2x0 C. in N,N-dimethylformamide solution) obtained by the polymerization of a monomer mixture comprising from 10 to 40% by weight of acrylonitrile, from 60 to 90% by weight of styrene, and from 0 to 20% by weight a monomer copolymerizable therewith, totaling 100% by weight.